Temperature measurement in turbulent flow is required in many industries, from avionics to HVAC to chemical manufacturing. In many applications, temperature is a critical parameter that must be monitored or measured as accurately as possible. These turbulent temperature measurements are commonly performed using cold-wire anemometers. A cold-wire typically consists of a wire filament designed to adapt to the ambient temperature with a resulting change of its resistance. The temperature of the fluid is generally related to the resistance of the wire through a static calibration method. However, any static calibration implicitly assumes that the sensitivity is independent of frequency, that is, that the frequency response is flat.
It is well known that the frequency response of a cold-wire is affected by the heat transfer from the sensing element or wire to the stubs, from the stubs to the prongs, and from the prongs to the probe body itself, a phenomenon known as end-conduction. A recent study has shown that this effect is more severe than previously thought, and can lead to significant measurement errors. A typical approach to solving this is to simply make the wire length-to-diameter aspect ratio, l/d, very large to avoid such end-conduction effects. However, since the smallest diameter used, typically, is on the order of 1 μm, this implies that the wires need to be on the order of a millimeter. Although a long wire reduces the end-conduction, the spatial resolution is also reduced. Other studies have pointed out that minimizing end-conduction effects can result in an increase of the total error due to spatial filtering. One study, using a cold-wire with 0.63 μm diameter and l/d=1500, estimated that the scalar dissipation was underestimated by approximately 30%.
Therefore, there is a need for a sensor capable of more accurately measuring temperature in turbulent flow.